1. Field of the Invention
The present invention relates to a method for producing proteins comprising nonprotein amino acids or alloproteins. From another view point, the present invention relates to a method for substituting a part of amino acids comprising a given protein by nonprotein amino acids.
2. Prior Art
It is being appreciated according to disclosures in numerous literature, specifications of patent publications or the like that a technology for producing desired gene products in abundance is on the way to be established by means of DNA recombination techniques. Furthermore, by addition of appropriate manipulations to a base sequence of a desired foreign gene, it has become possible to partially change an amino acid sequence or an amino acid composition of a desired natural protein. Consequently, the usefulness and effectiveness of desired gene products are enhanced. Additionally, proteins whose natural amino acids or protein amino acids have been artificially replaced can serve as materials, for example, for investigations of structure-activity correlations or mechanisms of biological functions. Thus, a method for producing such proteins will contribute immensely to both industrial and academic fields.
However, as long as the gene manipulation techniques mentioned above are to be used, all amino acids constituting a resultant gene product must be selected restrictively from 20 natural amino acids, namely glycine, alanine, valine, leucine, isoleucine, serine, threonine, aspartic acid, glutamic acid, asparagine, glutamine, lysine, arginine, cysteine, methionine, phenylalanine, tyrosine, tryptophan, histidine and proline. In other words, it is impossible to produce a protein which comprises nonprotein amino acids.
On the other hand, another method for producing proteins is that by chemical synthesis. Recently, techniques of chemical synthesis have been rapidly advanced so that it has become possible to synthesize long chain peptides using this method. According to this method, it is not at all difficult to synthesize peptides containing various nonprotein amino acids. However, it is substantially impossible to provide such long chain peptides using this method in an abundant amount for industrial and academic uses since the yield markedly decreases generally with extension of the chain length.
Therefore, development of a method for producing proteins containing nonprotein amino acids is now being expectantly hoped for.